<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <button type="button" onclick="uppic()">上传文件</button>
    <input type="file" style="display: none;">

    <script>
        var file = document.querySelector('input')
        function uppic(){
            file.click()
        }
    </script>
</body>
</html>